Combined effects of micro-silica and nano-silica on durability of mortar

To investigate the combined effects of micro-silica (MS) and nano-silica (NS) on the durability of concrete, an experimental program was launched, in which mortar mixes representing mortar portions of concrete with various water, MS and NS contents but a constant workability were made for strength, sulphate attack, carbonation, rapid chloride permeability and water absorption tests. It was found that the addition of MS and/or NS was effective in improving the durability of mortar. Moreover, for enhancing the strength, sulphate resistance and carbonation resistance, 1% NS was almost as good as 10% MS and the combined addition of MS and NS showed certain synergistic effects in the sense that the combined effects were larger than the respective sums of the individual effects. However, for enhancing the chloride resistance and water resistance, 1%-2% NS was less effective compared to 10% MS probably because the filling effect of 1%-2% NS was not as good as that of 10% MS. These results suggest that NS should not be added alone but should be added together with MS for best overall performance. (C) 2017 Elsevier Ltd. All rights reserved.